The May 2011 to April 2012 heat wave bumped the last record-setting warm year out of the way, which was November 1999 to October 2000

The National Oceanic and Atmospheric Administration (NOAA) has found that the last 12 months have been a record-breaking time period for warm weather in the U.S.

According to the NOAA's National Climatic Data Center, the 12-month time period from May 2011 to April 2012 has been the warmest consecutive string of months since 1895, which is when weather records began.

Over the past year, the U.S. has had its second hottest summer, warmest March and fourth warmest winter on record. It was also discovered that April 2012 was the third warmest ever, with 332 locations in the U.S. experiencing their warmest April temperatures on record.

About 22 states in the U.S. experienced their warmest year over the last 12 months. Many of the states were in the Northeast and Upper Midwest United States.

Also, cities like Washington D.C., Atlanta, Boston, Buffalo, New York City, Detroit, Chicago, New Orleans, Philadelphia, Tampa and Nashville have encountered their warmest start to the calendar year 2012. Twenty-six states east of the Rocky Mountains have recorded the beginning of 2012 as their warmest start of the year yet, with the lower 48 states experiencing temperatures about 5.4 degrees Fahrenheit above average so far.

A few examples of record-breaking states include North Dakota, which has had temperatures 10.4 degrees above normal so far this year; Minnesota, with 9.6 degrees above normal; South Dakota, with 9 degrees over average; Wisconsin, with 8.6 degrees above normal, and Iowa, with 8.6 degrees over average.

According to the NOAA, the cause of the warm weather is a jet stream pattern that has locked the cold air in the high latitudes and created "heat domes" over the center of the lower 48 states. These domes have wandered east and west periodically.

The May 2011 to April 2012 heat wave bumped the last record-setting warm year out of the way, which was November 1999 to October 2000. The average temperature was 2.8 degrees F above average at that time.